The treatment of aneurysms and other similar vascular disorders often involves the placement of microcoils within a space formed by the aneurysm. This space is often spherical, but in some instances can be elliptical or can have two or more lobular protrusions (often called bi-lobed or multi-lobed aneurysms). Most current microcoil systems have a variety of shapes and can include framing, filling and finishing coils. A framing coil is the first coil placed within an aneurysm and has a complex or three-dimensional shape designed to fit within the space formed by the aneurysm. The framing coil can be used to perform the following functions: (1) provide a stable frame within the confines of the aneurysm into which subsequent coils can be placed; (2) provide adequate loop coverage across a neck of the aneurysm; and (3) prevent loops from crossing the center of the aneurysm (which can create compartments within the aneurysm that require additional catheter manipulation, prolonging the procedure and increasing the risk of aneurysm rupture). Additionally, in some instances, it is desirable for the framing coil to be delivered with minimal or acceptably low friction within a microcatheter. Many framing coils have spherical shapes that can perform these functions when treating a spherical aneurysm; however, they are often inadequate when the aneurysm is non-spherical (e.g., elliptical or bi-lobed). Other framing coils have complex shapes that fit within non-spherical aneurysms; however, such coils typically consist of loops that are arranged with independent axes and are designed to be constrained by the aneurysm itself. This type of shape results in the framing coil having significant potential energy, meaning, for example, that in its unrestrained state it expands well beyond the dimensions of the aneurysm and therefore transfers force directly to the aneurysm wall when constrained in the space. While this force may not be enough to harm the aneurysm wall, it leaves the framing coil in a state susceptible to movement upon placement of subsequent coils. Often times, such coils will shift and potentially cause a loop to protrude into the parent artery, which requires adjunctive and/or emergency therapy. Additionally, the complex shapes of some framing coils often increase the friction created when they are delivered through a microcatheter.
Accordingly, needs exist for improved embolic framing microcoils.